The reading of electrical energy, water flow, and gas usage has historically been accomplished with human meter readers who came on-site and manually documented meter readings. Over time, this manual meter reading methodology has been enhanced with walk by or drive by reading systems that use radio communications to and from a mobile collector device in a vehicle. Recently, there has been a concerted effort to accomplish meter reading using fixed communication networks that allow data to flow from the meter to a host computer system without human intervention.
Fixed communication networks can operate using wire line or radio technology. For example, distribution line carrier systems are wire-based and use the utility lines themselves for communications. Radio technology has tended to be preferred due to higher data rates and independence from the distribution network. Radio technology in the 902-928 MHz frequency range can operate without an FCC license by restricting power output and by spreading the transmitted energy over a large portion of the available bandwidth.
Automated systems, such as Automatic Meter Reading (AMR) and Advanced Metering Infrastructure (AMI) systems, exist for collecting data from meters that measure usage of resources, such as gas, water and electricity. Such systems may employ a number of different infrastructures for collecting this meter data from the meters. For example, some automated systems obtain data from the meters using a fixed wireless network that includes, for example, a central node, e.g., a collection device, in communication with a number of endpoint nodes (e.g., meter reading devices (MRDs) connected to meters). At the endpoint nodes, the wireless communications circuitry may be incorporated into the meters themselves, such that each endpoint node in the wireless network comprises a meter connected to an MRD that has wireless communication circuitry that enables the MRD to transmit the meter data of the meter to which it is connected. The wireless communication circuitry may include a transponder that is uniquely identified by a transponder serial number. The endpoint nodes may either transmit their meter data directly to the central node, or indirectly though one or more intermediate bi-directional nodes which serve as repeaters for the meter data of the transmitting node.
Some networks may employ a mesh networking architecture. In such networks, known as “mesh networks,” endpoint nodes are connected to one another through wireless communication links such that each endpoint node has a wireless communication path to the central node. One characteristic of mesh networks is that the component nodes can all connect to one another via one or more “hops.” Due to this characteristic, mesh networks can continue to operate even if a node or a connection breaks down. Accordingly, mesh networks are self-configuring and self-healing, significantly reducing installation and maintenance efforts.
Some AMI or AMR systems use a mobile collection device, such as a handheld computer equipped with RF technology or a van based RF system, to collect meter data. Communications are conducted between the collection device through repeaters to endpoint nodes. Data can be extracted from mesh networks using a number of different communication protocols. Some examples include a one-way protocol (also known as a bubble up protocol), a one-and-a-half-way protocol (also known as a 1.5-way protocol or a wake up protocol), and a two way protocol. In the one-way or bubble up protocol, the transponder in each MRD broadcasts its meter read data in such a way that the mobile collection device only needs to listen to receive the data. In the 1.5-way or wake up protocol, the mobile collection device broadcasts a wake up tone on a designated frequency. Any MRD within receiving range of the wake up tone will respond with its meter read data. In the two-way protocol, the mobile collection device transmits commands that are directed to particular MRDs. For example, the mobile collection device may use commands that include the serial numbers of transponders of the MRDs to which the commands are directed. In the two-way protocol, each MRD only responds to commands that include its transponder's serial number and ignores other commands. In this way, the mobile collection device selectively targets certain MRDs for downloading meter read data.
The 1.5-way and two-way protocols described above involve using polling techniques to pull data from an endpoint node to the central node via a predefined path. The path from an endpoint node to the collection device can have a relatively large number of repeaters. When polled communications are attempted for endpoint nodes that are several hop levels away from the collection device, outbound and inbound packets have built in redundancy to improve the probability of successful end-to-end communication. For example, when an endpoint node is eight hop levels away from a collection device, some conventional polled communication techniques involve automatically retrying each outbound and inbound packet three times to increase the probability that the packet will be successfully transmitted. This “brute force” method is quite effective in ensuring successful end-to-end communication, but consumes available bandwidth.
Accordingly, a need exists for a technique for promoting successful end-to-end communication in a polled mesh network while improving system throughput.